(1) Conventional Mobile Communication System
In a Long Term Evolution (LTE) system, usually a network centralized control mode is adopted, i.e., as shown in FIG. 1, uplink and downlink data for a User Equipment (UE) is transmitted and received respectively under the control of a network (e.g., the UE may communicate with a core network via an evolved NodeB (eNB)). In addition, the data between the UEs is also forwarded and controlled via the network. Hence, there is no direct communication link between the UEs, and the UE is not permitted to transmit the uplink data by itself.
(2) D2D Proximity Service
In a future mobile communication system, a D2D direct communication mechanism is introduced, so as to meet users' requirements in a better manner and improve the information exchange efficiency.
As stipulated by the 3rd Generation Partnership Project (3GPP), the D2D proximity service includes D2D Discovery and D2D communication between mobile devices, which will be described hereinafter.
For ProSe Discovery, the UE may determine, using Evolved Universal Terrestrial Radio Access (E-UTRA), that another UE is located in proximity thereto. For example, on the basis of the ProSe Discovery, the D2D UE may find a taxi or a friend located in proximity thereto.
For ProSe Communication, a link may be directly established between two adjacent UEs (as shown in FIG. 2), so as to convert a communication link via a network into a local, direct communication link, thereby to save the bandwidth and improve the communication efficiency. Or, the direct communication link may be established between the two adjacent UEs, so as to acquire a stable, high-speed and economic communication service. The ProSe Communication is usually controlled or assisted by a network side, and even resources may be dynamically allocated by the eNB to the UEs for the ProSe Communication. A signaling link in FIG. 2 includes a link for direct communication between the devices (i.e., a D2D link) and links between the devices and a network node (i.e., device-to-node (D2N) links).
Radio resources for the ProSe Discovery and ProSe Communication may be allocated in a resource pool-based mode, i.e., the UE that needs the radio resources for the ProSe Discovery or ProSe Communication may select the radio resources from a resource pool in accordance with a certain rule. The ProSe Discovery and ProSe Communication may use non-dedicated radio resources, i.e., they may share the radio resources with an LTE cellular network.
For the D2D discovery, the UE may determine the resource for transmission in two modes, i.e., a UE autonomous selection mode in which the UE may initiatively select a resource from the resource pool for the data transmission, and a network scheduling mode in which the UE may transmit the data on a resource allocated by a base station.
The above-mentioned UE autonomous selection mode and the network scheduling mode have their own advantages and disadvantages. For example, for the UE autonomous selection mode, the UE may initiatively select the resource in accordance with a monitoring result. However, in the case that there are a large number of users or there is a strong interference, the UE may have a long waiting or backoff time, and the quality of service (QoS) may be adversely affected. For the network scheduling mode, control signaling overhead in the network may increase. In a word, the UE autonomous selection mode and the network scheduling mode may be applied to different scenarios, and the D2D communication will be adversely affected in the case that the resource allocation modes cannot be switched flexibly in accordance with the practical need.
Similarly, for the D2D communication, there also exist different resource allocation modes (i.e., the above-mentioned UE autonomous selection mode and network scheduling mode may also be used), and also there is currently no effective way for the flexible switch between these resource allocation modes.
Hence, there is an urgent need to provide a solution for enabling the UE to be efficiently switched between different resource allocation modes.